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VOR/ILS  
User currently offlineZvocio79 From United States of America, joined Nov 2006, 172 posts, RR: 0
Posted (8 years 2 weeks 2 days 23 hours ago) and read 6188 times:

Can the VOR tx/rcv be used as a runway localizer on a ILS approach? how does that work? I've seen a certified IFR craft with a glide slope antenna only and I was wondering how do they get a runway locelizer frequency. Thank You guys........and girls.

11 replies: All unread, jump to last
 
User currently offlineXXXX10 From United Kingdom, joined Jan 2000, 777 posts, RR: 0
Reply 1, posted (8 years 2 weeks 2 days 22 hours ago) and read 6182 times:

I am sure some one better qualified than I will answer this but until then:

I believe there are VOR or NDB approaches using DME, marker beacons or waypoints to mark disance to go on approach.Or alternatively a localiser.

A glideslope only approach would also need a VOR or NDB for lateral guidance on approach.

An approach using just a VOR or NDB would require the a/c to fly a timed down-wind leg unless of course they can be given distance to go information by the tower using the radar.

Please feel free to correct me if I am wrong.

[Edited 2006-11-08 10:08:42]

User currently offlineRendezvous From New Zealand, joined May 2001, 518 posts, RR: 0
Reply 2, posted (8 years 2 weeks 2 days 21 hours ago) and read 6165 times:

VOR is less accurate than a localiser. In smaller aircraft (ie, C172 with vor/ils) I think the localiser is picked up with the VOR antenna, whereas the glideslope must use the glideslope antenna because it is in a vertal sense rather than horizontal.

User currently offlineTroubleshooter From Germany, joined Feb 2005, 423 posts, RR: 4
Reply 3, posted (8 years 2 weeks 2 days 21 hours ago) and read 6164 times:

For an ILS approach you need an ILS receiver tuned to an ILS frequency. A VOR receiver can not receive or compute ILS signals. The ILS receiver is tuned to a localizer signal. Automatically a dedicated glideslope frequency is tuned. Both signals are received and a deviation is calculated (amongst other things) for display to the flight crew. A VOR receiver can not do this calculation! But a VOR antenna can receive the localizer signal as this is working in the same frequency range as a VOR.

The B737NG for example uses a combined VOR/localizer antenna on top of the vertical stabilizer. It receives VOR stations enroute and receives the localizer signal during the initial approach if it is tuned to do so. When the crew selects approach (APP) or localizer (LOC) mode on the mode control panel and an active ILS frequency is tuned an automatic transfer to the localizer antenna inside the radome happens.

Hope this helps. I also stand corrected if someone with deeper knowledge of these systems finds any mistakes.



This job sucks!!! I love this job!!!
User currently offlineCurmudgeon From Australia, joined Oct 2006, 695 posts, RR: 22
Reply 4, posted (8 years 2 weeks 2 days 20 hours ago) and read 6153 times:

You only get glideslope information on a full ILS approach. There is NO vertical approach slope guidance on a non precision (NDB, VOR, LOC/BC approach.


Jets are for kids
User currently offlineIAHFLYR From United States of America, joined Jun 2005, 4790 posts, RR: 22
Reply 5, posted (8 years 2 weeks 2 days 19 hours ago) and read 6147 times:

Quoting Troubleshooter (Reply 3):
The B737NG for example uses a combined VOR/localizer antenna on top of the vertical stabilizer. It receives VOR stations enroute and receives the localizer signal during the initial approach if it is tuned to do so.

NG's should be receiving signals from satellites as GPS is their primary nav source......so if an RNAV approach is in place to the runway, providing localizer like guidance there is your approach with the localizer out. If there is a very tight RNP value to an RNAV approach with VNAV then you can get down to almost CAT I ILS minimums if the crew and craft is certified for that.



Any views shared are strictly my own and do not a represent those of any former employer.
User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 6, posted (8 years 2 weeks 2 days 12 hours ago) and read 6061 times:

Quoting Troubleshooter (Reply 3):
For an ILS approach you need an ILS receiver tuned to an ILS frequency. A VOR receiver can not receive or compute ILS signals. The ILS receiver is tuned to a localizer signal. Automatically a dedicated glideslope frequency is tuned. Both signals are received and a deviation is calculated (amongst other things) for display to the flight crew. A VOR receiver can not do this calculation! But a VOR antenna can receive the localizer signal as this is working in the same frequency range as a VOR.

Not entirely true...a VOR receiver, by design, will also receive the localizer portion of an ILS. So, as long as an ILS approach has an associated LOC (localizer only-left/right guidance), you may still shoot the approach using a VOR receiver (to localizer minimums, which are typically much higher than with LOC/Glideslope guidance). The phase shift principle used by the VOR receiver is the same for a localizer-the difference is that, when tracking a LOC, the receiver ignores the Omni Bearing Selector (OBS) setting.

LOC frequencies are tunable by every VOR receiver ever made (and, to the original poster, there is to transmit function on a VOR receiver The only transmitting involved is if you are using DME, or Distance Measuring Equipment, which is another beast entirely). The LOC will be received by the aircraft's VOR antenna, as LOC frequencies occupy the lower portion of the NAV frequency band (108.1 Mhz-117.9 Mhz). As I recall, in the US at least, 109.1-111.9 Mhz is reserved for localizers.

The Glideslope portion is automatically tuned by an ILS receiver, as there is a standard frequency pairing for glideslopes/localizer frequencies (and I believe, IIRC, the glideslope is up in the 300 Mhz frequency range...correct me as necessary). An ILS receiver is also, by nature, a VOR receiver. However, a VOR receiver, with no glideslope, would not provide you with full ILS capability (no glideslope-but you would be able to shoot many ILS approaches to LOC minimums).

A Localizer is much more sensitive than a VOR, however, and it has to be: it is trying to direct an aircraft towards a runway in some pretty bad visibility

Good references:

http://en.wikipedia.org/wiki/Instrument_Landing_System
http://en.wikipedia.org/wiki/Localizer
http://en.wikipedia.org/wiki/VHF_omnidirectional_range

[Edited 2006-11-08 19:36:26]


Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineAvioniker From United States of America, joined Dec 2001, 1109 posts, RR: 11
Reply 7, posted (8 years 2 weeks 2 days 11 hours ago) and read 6032 times:

Localizer uses audio frequency on the VHF carrier to keep you on the centerline. Its origin is in a pilot wearing a headset hearing the 90 and 150 hz tones and keeping them at a balanced level in his head. If one got louder he would steer away from it to balance the volume levels. Same thing for the glide slope. Vor uses a rotating beacon output at a predetermined level of attenuation depending on the radial or your relative bearing you're flying and receiving it from or on.
A VOR receiver can receive the ILS signal but has no capability to balance the tones therefore you can't use a VOR-only receiver to fly an ILS unles there's a VOR component to the Localizer facility which is rare. You'd simply be riding the beam much like an ADF.
Also the Localizer antenna is at the departure end of the runway so that the pilot using it has steering direction throughout the landing and roll out.
The Glideslope antenna is at the approach end of the runway and is bounced off the ground in front of the antenna to give a true 0 ft. altitude reference.
That's why a back course approach is never flown with glide slope.
As to the GPS being the primary means of navigation, it's a customer decision at the time the software load is determined. Some still use DME and others IRS/INS with the other navigation media as secondary/tertiary.
Oh nuts my fingers are tired, here
http://www.navfltsm.addr.com/vor-nav.htm

Blue on top. . .
 Smile



One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 8, posted (8 years 2 weeks 2 days 11 hours ago) and read 6022 times:

Avioniker is the most accurate so far. KELPkid, the VOR uses a phase differential between the reference phase and the variable phase, but the localizer is quite different in that it looks at DDM, difference in depth of modulation, as Avioniker said, comparing the relative strengths of the 90 and 150 hz modulation, exactly the same way the glideslope does it. The main difference being that while the localizer carrier frequency is 108 to 118 Mhz (same as VOR) the GS is indeed in the mid 300 Mhz range. It's the carrier frequency that decides which antenna and receiver are used for what. For example the lowly marker beacon is 75 Mhz, and therefore needs it's own antenna and receiver.

User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 9, posted (8 years 2 weeks 2 days 10 hours ago) and read 6008 times:

Quoting Avioniker (Reply 7):
Localizer uses audio frequency on the VHF carrier to keep you on the centerline. Its origin is in a pilot wearing a headset hearing the 90 and 150 hz tones and keeping them at a balanced level in his head.

Is this on the FM carrier, then? On the AM carrier (which you listen to in the cockpit when you select "IDENT" on the appropriate radio), all you hear is the Morse code station identifier...

Quoting Avioniker (Reply 7):



Quoting Avt007 (Reply 8):

Thanks for the corrections, guys. Learn something new every day... just got a question: are there any common VOR receivers out there that don't decode the LOC by default? Even the Sporty's pilot shop air band transceiver (a great backup tool!) will show you your Localizer deviation  Smile [Very cool!]



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineAvioniker From United States of America, joined Dec 2001, 1109 posts, RR: 11
Reply 10, posted (8 years 2 weeks 2 days 8 hours ago) and read 5987 times:

I'm pretty sure that when the tubes went away so did your ability to buy an exclusive receiver.
If you tune up a VOR or ILS frequency on a straight AM radio you'll hear everything at once. The Nav receivers have discriminators to separate the signals. To say you hear the Ident on the AM portion, while true, is an oversimplification and I've been trying to get a group of highly educated, very intellegent, ultimately qualified (just in case some of them see this) technicians to understand this subject all week.
I'm going to go and watch some mindless TV entertainment through the bottom of an amber bottle now.
Cheers
 Smile



One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 11, posted (8 years 2 weeks 2 days 6 hours ago) and read 5942 times:

I hear you, Avioniker. I had a fun time a while ago trying to get across the concept of the parity bit in the ARINC 429 data word. Teaching is a lot of fun,and educational for the instructor as well.

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